1. Field of the Invention
The present invention generally relates to wireless communications and more particularly to changing radio frequency (RF) emission patterns with respect to one or more antenna arrays.
2. Description of the Prior Art
In wireless communications systems, there is an ever-increasing demand for higher data throughput and a corresponding drive to reduce interference that can disrupt data communications. For example, a wireless link in an Institute of Electrical and Electronic Engineers (IEEE) 802.11 network may be susceptible to interference from other wireless access points and stations, radio transmitting devices in the vicinity of the network, and changes or disturbances in the wireless link environment between an access point and remote receiving node. In some instances, the interference may degrade the wireless link thereby forcing communication at a lower data rate. The interference may, in some instances, be sufficiently strong as to disrupt the wireless link altogether.
One solution is to utilize a diversity antenna scheme. In such a solution, a data source is coupled to two or more physically separated omnidirectional antennas. An access point may select one of the omnidirectional antennas by which to maintain a wireless link. Because of the separation between the omnidirectional antennas, each antenna experiences a different signal environment and corresponding interference level with respect to the wireless link. A switching network couples the data source to whichever of the omnidirectional antennas experiences the least interference in the wireless link.
Notwithstanding, many high-gain antenna environments still encounter—or cause—electromagnetic interference (EMI). This interference may be encountered (or created) with respect to another nearby wireless environments (e.g., between the floors of an office building or hot spots scattered amongst a single room). In some instances, the mere operation of a power supply or electronic equipment can create electromagnetic interference.
One solution to combat electromagnetic interference is to utilize shielding in or proximate an antenna enclosure. Shielding a metallic enclosure is imperfect, however, because the conductivity of all metals is finite. Because metallic shields have less than infinite conductivity, part of the field is transmitted across the boundary and supports a current in the metal. The amount of current flow at any depth in the shield and the rate of decay are governed by the conductivity of the metal, its permeability, and the frequency and amplitude of the field source.
With varying locations of devices communicating with omnidirectional antennas and the varied electromagnetic interference in most environments, it is desirable to have control over an emitted radiation pattern to focus the radiation pattern where it would be most useful.